Process for the production of granulated materials

ABSTRACT

One or more ingredients which could be agglomerated and preferably enter into the composition of a fertilizer mixture are subjected to the action of positive external forces, such as shearing, smearing and pressing in order to superficially treat the surface thereof. The solid particles are mixed with a liquid phase such as water, nitrogeneous, phosphatic and potassic solutions and acids prior to the above treatment. Thereafter the mixture so treated is granulated, dried and cooled to give a homogeneous and uniform composition.

United States Patent Bolduc [4 1 Mar. 14, 1972 [54] PROCESS FOR THEPRODUCTION OF GRANULATED MATERIALS Camillien Bolduc, 320 Thomas PepiaStreet, Boucherville, Quebec, Canada Aug. 17, 1970 Related US.Application Data [72] Inventor:

Filed:

Appl. No.:

[63] Continuation-in-part of Ser. No. 614,189, Feb. 6,

US. Cl ..71/64 DA, 23/313 Int. Cl. ..C05b 19/00 Field of Search ...7l/64DA, 64 DC; 23/313 [56] References Cited UNITED STATES PATENTS 2,287,7596/1942 Handesty etal. ..75/64 2,893,858 7/1959 MacDonald et al. ..7l/642,935,387 5/1960 Phillips ....7l/64 DC 3,523,784 8/1970 Coon ....71/64DA 3,385,660 5/1968 Dunseth ..71/64 DA Primary Examiner-Reuben FriedmanAssistant Examiner-Richard Barnes Attorney-Raymond A. Robic [57]ABSTRACT 3 Claims, 2 Drawing Figures lLu DRYFR CROSS-REFERENCE Thisapplication is a continuation-in-part of application, Ser. No. 614,189,filed Feb. 6, 1967 and now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention isdirected to a process for the production of granulated materials. Moreparticularly, the invention is concerned with an improved process ofmanufacturing complex fertilizers. Preferably, the present inventionrelates to an improved process for the manufacture of granulatedfertilizers having an unusually high degree of uniformity of granularsize and of chemical composition.

2. Description of the Prior Art The commercially available granulatedfertilizers are usually characterized by the fact that the differentsize particles do not possess uniformity of chemical composition. Thissituation may be exemplified by the following analyses made on fourscreen fraction of various commercially available fertilizers.

PRODUCT A Mesh Z P,0, 14,0

Average: 19.44 19.93

Fraction in agreement with average analysiswithin acceptable tolerances:None.

PRODUCT B Mesh Z N P 0, K,0

Average 4.41 20.09 19.22

Fraction in agreement with average analysiswithin acceptable tolerances:None.

PRODUCT C Mesh 1 N F30 K,0

Average 6.48

Fraction in agreement with average analysiswithin acceptable tolerances:None.

This situation generally results in excessive segregation in storagebins and during handling, with correspondingly excessive variations inchemical composition and difficulty in meeting the guaranteed analyses.

The commercial processes for manufacturing N-P O -Kp fertilizersessentially comprise the following steps: screening, weighing and mixingof the solid ingredients, ammoniationgranulation, drying, cooling andclassifying. The ammoniation-granulation step can be carried out in oneor two operations. The ammoniation consists in reacting nitrogenousproducts such as anhydrous ammonia, ammonia solutions, ammonia-ammoniumnitrate solutions, ammonia-arnmonium nitrate-urea solutions with acidicproducts comprising mainly sulphuric and/or phosphoric acids, singleand/or triple superphosphates. The reactions are carried outcontinuously or in batch mixers. The heat of reaction which is generatedaccelerates the agglomeration process and the formation of granules. Inthe prior practices, the granulation process is usually performed bycascading the particles in rotating drums or submitting the particles tothe action of the pug mills helicoidal screw device. Ammoniation isusually carried out in the same apparatus. The typical prior artpractice is well exemplified by the fertilizer granulation process ofthe MacDonald et al., U.S. Pat. No. 2,893,858 in which the solidingredients are agitated in either a rotary drum or a pug millapparatus. Similarly, Hardesty et al., U.S. Pat. No. 2,287,759 alsoteaches that granulation may occur in a rotary drum apparatus. In theserotary or pug mill granulators, the solid particles of fertilizer arefree to roll on the interior surface of the rotary cylinder and are in arelatively free condition, each ingredient having its own rate ofagglomeration. The products characterized by a large range of sizes andchemical compositions, and it is therefore necessary in all commercialinstallations to submit these products, after proper drying and/orcooling, to an extensive classification. Both the fines and the coarseparticles are returned to the first step of the process since only anarrow range of particle size is suitable for commercial purposes. It isthus necessary to recycle important quantities of materials and, forthat purpose, it is common practice to have a recycling load having avolume of at least six times the volume of finished product.

It is often difficult, if not impossible, under practical operationconditions to reach equilibrium in the system and to maintain a constantchemical composition of the end products unless large quantities of fineand coarse fertilizer particles are recycled.

It is also well known that potash is particularly difficult toincorporate into the granules especially when it is in large proportion.Furthermore, potash alone cannot be agglomerated by the conventionalprocess.

In the conventional rotary drum method of granulating fertilizers, eachconstituent tends to agglomerate according to a specific particular ratein a manner only slightly influenced by the presence of otherconstituents and mostly independent of the basic ratio of N-P-K of thefertilizer formula. As a consequence, in a conventional drum granulator,the analysis results of the particles having different sizes at the exitof the granulator are widely spread.

It has been realized that particles of different sizes and chemicalcompositions, as produced by the processes of the prior art, tend tosegregate easily during handling and stock piling. This is a widelyrecognized fact in the fertilizer industry. Segregation of the particlescauses errors in the product analysis, since it makes representativesampling extremely difficult and often impossible. To partly counteractthe effects of segregation, it has been customary to add supplementalplant food or to overformulate the fertilizers, thus substantiallyincreasing the product costs.

It is therefore an object of the present invention to avoid differential agglomeration of the fertilizers constituents and to producegranules showing remarkably consistent chemical compositions betweenparticles of different sizes.

Another object of the present invention resides in the production ofuniform granules and in controlling the growth of the granules of therequired size.

It is yet another object of this invention to provide a uniform rate ofagglomeration of all constituents.

Another object is to obtain uniformity of chemical compositions betweenparticles of different sizes.

These and other objects according to the invention are attained in aprocess which comprises the mixing of at least one solid particlematerial with a liquid agent, submitting this mixture to the action ofcontinuous external, combined mechanical mixing, shearing, pressing andsmearing forces applied to the surfaces of the two phases to cause onlysuperficial wetting by the liquid phase of the total surface and of allthe solids. All the particles are thus completely coated with a film ofliquid.

As soon as the liquid film is formed on the surface of the solublesubstances, there appears a concentrated solution of that substancewhich, through the above forces, comes in contact with other film-coatedparticles and exchanges solutes. The net effect of these numerousexchanges is that in a very short period of time all particles becomecoated with a film of a concentrated solution of the same composition.lt has been determined experimentally that the minimum time required toachieve this uniform conditioning varies from 1 to 6 minutes dependinglargely on the rate of solubilization of the soluble substances presentin the mixture being conditioned, and the number of times the materialhas been submitted to the above forces. Efficient conditioning of allsurfaces according to the present invention can be carried out with theaid of a wheel that is free to rotate about its axis in order to producea friction with the material to be conditioned, with the wheel beingdriven mechanically around a circular path. The material to beconditioned is kept in a plane, by means of mixing plows constantlyreturning the material over into the path of the wheel. The action ofthe wheel is adjustable and there is no appreciable crushing of theparticulate materials; the actual load exerted by the wheel on thematerials may vary between 20-80 pounds/square inch.

The forces applied in the invention process are to be distinguished fromthe forces applied to the particles being treated by prior artapparatus, such as exemplified by the aforementioned MacDonald et al.,and l-lardesty et al. patents. In the invention process, the particlesare static when the smearing and pressing forces are applied by theaction of the conditioning wheel. in the rotating or pug mill apparatusof the prior art, the applied forces vary in magnitude since they actupon moving particles as such, the degree of homogeneity of agglomeratedparticles and the overall efficiency of granulation of these prior artapparatus are much less favorable than the homogeneity and efficiencyachievable through the process of the instant invention.

After proper conditioning by the wheel, the ingredients of the inventionare transferred to a rotary drum for granule formation. This stepdiffers from the prior art in that it is much more efficient with almost100 percent of all the particles, conditioned statically as previouslydescribed, agglomerating in the right proportion whereas, in the priorart, the agglomeration is only 10 to percent, thus necessitatingextensive classification and large recycling of nonagglomeratedparticles. Furthermore, according to the invention, the agglomeratedparticles have an outstanding homogeneous chemical composition.

These two latter points are exemplified in the following table bycomparing a few fertilizer compositions manufactured by the prior artand by the invention process respectively.

Comparison of products as taken from granulator:

Sum of screen fractions in 2-16-6 9L0 12.6 99.7 20.7 3-12-12 97.7 12.098.2 45.0 4-24-20 97.0 16.8 95.7 0.0 5-20-10 86.8 12.2 98.3 0.0 6-l2-l 294.8 18.9 94.8 0.0 8-l6-l6 99.1 I51 99.] 0.0 10- l0-l 0 97.8 13.2 99.00.0

The following example gives the effect of the pressure expressed inpounds per square inch on the granulation efficiency of the invention.The granulation efiiciency is the percentage of particles of acceptablesize after being processed by the invention process. This example islimited to two grades, viz 9:20:29 mu l-2 0:20;

Pressure Efficiency lb./sq.in. it

64 (compaction) For a specific comparison between the prior artprocesses and the invention process which employs the application ofmuch greater forces upon a bed of static particles, the following tableis provided giving a comparison of pressure versus granulationefficiency for these processes:

Granulation efficiency is again defined as the percentage of particlesof acceptable size, i.e., 6 20 Tyler standard sieve.

The granule formation step according to the invention provides apositive control on the growth of the granule since the concentratedfilm described previously is easily evaporated by the application ofheat, causing the mechanism of agglomeration to stop, and thuspermitting a positive control on the size of the granules.

According to the invention, any liquid such as water, nitrogeneous,phosphatic or potassic solutions, acids or any mixture thereof may beused.

The following substance or any mixture thereof may be agglomerated:muriate of potash, sulphate of potash, ammonium, sulphate, singlesuperphosphate, triple superphosphate, ammonium phosphates, etc. it is,however, obvious that this process can be applied to any chemicalcompound which is susceptible to granulation.

In summary the essential differences between the process of theinvention and the prior art are:

The formation of a concentrated film solution of uniform composition onthe total surface area of all the constituent solid particles. In theprior art, the particle surfaces are only partly covered and the surfacesolution is of non uniform composition and concentration.

The agglomeration rate is the same for all the constituents and in aratio corresponding to the average composition of the mixture. This isdifierent from the prior art where the particles agglomerate atdifferent rates and in an undetermined ratio as shown by the largevariation of sizes and composition resulting from the agglomeration.

The positive control of granule size without the aid of screens whereasin the prior art only extensive screening can control the granule size.

In my process wherein there is practically 100 percent agglomeration,there is obtained a high degree of homogeneity which makes it possibleto eliminate to a large extent the overformulation of the fertilizers.

Since the composition of the products produced by the process of myinvention is not altered or changed even if they are allowed tosegregate there is an important economy of labor costs in the trimmingand the handling of the fertilizers.

Since the fertilizers are outstandingly homogenous with respect to sizeand chemical compositions, the sampling for analysis is much simpler.

It will be realized that in a plant production of fertilizer granulesaccording to the process of my invention, the feeding of the dryer with100% granular materials will result in more efficient use of fuel, nothaving to dry a large amount of fines. The size of the dryer couldtherefore be substantially reduced.

The loss of fertilizers as dusts is substantially reduced and the costof the dust handling equipment is substantially minimized.

Other substantial economy can be realized in the size of the screeningsurface, the size of the cooler, of the conveyor and the handlingequipment in general. The amount of fuel is also substantially reducedsince a smaller liquid phase is required to achieve the agglomeration.

It is the combined action of the intensive mixing, shearing and pressingforces, applied externally to the surface of the solids and the liquidindividual components ofa given mixture, which provide a full andcomplete wetting of all these surfaces. As a result, there is produced amaximum quantity of soluble solids passing into solution in a givenperiod of time. It is also possible that, even after two particles areadhesively bound together, there still remains large conditionedsurfaces for further agglomeration.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings which illustrate anembodiment according to the invention,

FIG. 1 is a diagrammatic illustration of the process according to theinvention; and

FIG. 2 depicts a conditioning wheel apparatus which can be used forsuperficially treating the surface of the particulate material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS:

Referring to the drawing in FIG. 1, it will be seen that preweighedsolid constituents are continuously or intermittently fed into anammoniator 1 where nitrogeneous constituents and acidic products arereacted together. The ammoniated mixture is thereafter continuously orintermittently transferred to a conditioning wheel apparatus 2 where itis submitted to the action of positive external forces of a magnitudemuch higher than those normally encountered in previously describedcommercial processes. At this stage, a liquid phase such as watersolutions of nitrogeneous, phosphatic and potassic salts or an acid orany mixture thereof is added. The mixture, after having been conditionedwith this liquid phase is continuously or intermittently transferred toa rotary granulator 3 where the granules grow to proper size. Finally,the granules are continuously or intermittently transferred to the dryer4 and then to a cooler 5.

The conditioning wheel apparatus according to the invention isparticularly described in FIG. 2. It comprises a reservoir 6 providedwith a conditioning wheel 7 which is adapted to produce a friction withthe material to be treated. The actual load exerted by the wheel may beadjusted by means of the adjustable weight 8. The device also comprisesa vertical shaft 9 mounted vertically in the center of the bottomsurface 10 of the reservoir 6. On the upper portion of the verticalshaft 9 there is provided transversely thereof a horizontal axle 11.

The conditioning wheel 7 is freely mounted at one end of said axle andthe weight 8 is adjustably mounted at the opposite end thereof.

On the top of the shaft 9 there is a bracket 12 fixedly mounted thereonto project outwardly therefrom. Secured to the outer end of bracket 12is an inverted T-member 13 which has a pair of plows or scrapers l4 and15 attached thereto. The material to be conditioned is kept in constantmotion within the bottom surface 10 of reservoir 6 by means of themixing plows or scrapers 14 and 15 which continuously return thematerial into the path of the conditioning wheel 7.

This process is suitable for the production of granules of one or anynumber of ingredients constituting the composition of the granules ofthe fertilizer. Particularly, it has been found that potash can verywell be agglomerated by using the process according to the invention.

However, it is obvious that the most practical application is theproduction of granulated fertilizers of the NP O -K O type in any ratioof individual raw materials.

The following table provides the comparative moisture percentagesrequired for superficial wetting in order to achieve granulation. Thereare averagesof two years operating conditrons.

Grade Moisture Invention Process, 7: Prior Art, 7: O-ZO-ZO 017 5.0(steam) O-l 5-30 1.0 5.5 (steam) 5-20-20 1.2 4.6 6-12-12 2.1 7.410-10-10 1.7 6.2 10-20-20 4.0 8.4 16-8-8 2.3 5.6

The following examples are given to illustrate some preferredembodiments of the invention.

EXAMPLE 10-20-20 Standard Tyler Mesh 2 E0, KJJ

Average: 20.0 20.7

The average analysis of fractions 6 10 mesh and 10 20 mesh of theresulting granules representing 97.9 percent of the product shows thatthey are within acceptable tolerances. This is a contrasting situationwith that of product A described earlier where none of the fractions arein agreement with the average analysis.

EXAMPLE 2 5-20-10 An ammoniating solution, single superphosphate,concentrated superphosphate and muriate of potash required to formulatea 5-20-10 were mixed, reacted and treated in the apparatus describedabove in a manner similar to Example 1. The product obtained, afterdrying, had the following analysis:

Standard In this second example, it will be seen that fraction 6 mesh,fraction -6 10 mesh and fraction -10 20 mesh represent 98.3 percent ofthe product. Each fraction is individually in agree ment within theacceptable tolerances and conforms with the average analysis of theproduct. This product is therefore not susceptible to segregationaccording to its composition.

EXAMPLE 3 8-l6-l6 An ammoniating solution, ammonium sulphate, singlesuperphosphate, concentrated superphosphate and muriate of potash inamounts required to formulate an 8-16-16 fertilizer were mixed, reactedand treated in the apparatus described above in a manner similar toExample 1. The product after drying, had the following analysis:

Standard Tyler Mesh 71 N P 0, X

Average: 7.83 16.05 16.6]

The above results indicate that 99.1 percent of the product are withinacceptable tolerances and meet the average analysis. The uniformity ofthe composition is also well illustrated by reference to the individualscreen fractions.

lclaim:

I. A process for the production of a N-P 0 -K 0 granulated fertilizerwhich comprises the steps of:

a. mixing with a liquid agent selected from the group consisting ofwater, nitrogeneous, phosphatic, and potassic solutions at least onesolid particulate material selected from the group consisting ofpotassic salts, nitrogeneous salts, phosphatic materials and mixturesthereof, whereby said liquid agent and said particulate material form aliquid phase and a solid phase,

b. forming a static bed of said liquid phase and said solid phase,

c. superficially treating the surface of said particulate material whilecontinuously mixing the same by shearing, smearing and pressing of saidparticulate material by the application of external forces of themagnitude within the range of 20-80 pounds per square inch to saidstatic bed to cause only superficial wetting of the total surface of theparticulate material and solubilization of soluble constituents of saidparticulate material, wherein the amounts of moisture to cause saidsuperficial wetting is within the range of 0.7 4.0 percent of saidparticulate material, whereby a concentrated solution of said solidphase is formed,

d. granulating said particulate material in the presence of heat tocontrol the uniform growth of the granulated particles such that 85percent of the granulated particles are within the range of 6 20 meshstandard Tyler sieve size, and

e. drying and cooling the granulated material.

2. A process for the production of granulated N-P 0 -K O fertilizerwhich comprises the steps of:

a. mixing with a liquid agent selected from the group consisting ofwater, nitrogeneous, phosphatic and potassic solutions, at least onesolid tparticulate material selected from the group consisting opotassic salts, nitrogeneous salts, phosphatic materials and mixturesthereof whereby said liquid agent and said solid particulate materialform a liquid phase and a solid phase,

b. superficially treating the surfaCe of said particulate material whilecontinuously mixing the same by shearing, smearing and pressing of saidparticulate material by the action of at least one rotating pressingdisc entering said phases, said shearing, smearing and pressingproducing positive external forces of the magnitude within the range of20 pounds per square inch applied to the surfaces of said two phases tocause only superficial wetting of the total surface of the particulatematerial and solubilization of soluble constituents of said particulatematerial wherein the amount of moisture to cause said superficialwetting of the total surface of the particulate material is within therange of 0.7 4.0 percent of said particulate material, whereby aconcentrated solution of said solid phase is formed,

c. granulating said particulate materials in the presence of heat tocontrol the uniform growth of the granulated material into particleswherein at least percent of the granulated particles are within therange of 6 to 20 mesh standard Tyler sieve size, and

d. drying and cooling the granulated material.

3. A process for the production of granulated materials which comprises:

a. mixing at least one solid particulate material selected from thegroup consisting of potassic salts, nitrogeneous salts, phosphaticmaterials and mixtures thereof with a liquid agent selected from thegroup consisting of water, nitrogeneous, phosphatic and potassicsolutions,

b. superficially treating the surface of said particulate material whilecontinuously mixing the same by applying thereto positive externalforces of from 20 80 pounds per square inch to cause only superficialwetting of the total surface of the particulate material andsolubilization of soluble constituents of said particulate materialwherein the amount of moisture to cause said superficial wetting of thetotal surface of the particulate material is within the range of 0.7 4.0percent of said particulate material, and

c. granulating said particulate material in the presence of heat tocontrol the uniform growth of the granulated particles.

2. A process for the production of granulated N-P205-K20 fertilizerwhich comprises the steps of: a. mixing with a liquid agent selectedfrom the group consisting of water, nitrogeneous, phosphatic andpotassic solutions, at least one solid particulate material selectedfrom the group consisting of potassic salts, nitrogeneous salts,phosphatic materials and mixtures thereof whereby said liquid agent andsaid solid particulate material form a liquid phase and a solid phase,b. superficially treating the surface of said particulate material whilecontinuously mixing the same by shearing, smearing and pressing of saidparticulate material by the action of at least one rotating pressingdisc entering said phases, said shearing, smearing and pressingproducing positive external forces of the magnitude within the range of20 - 80 pounds per square inch applied to the surfaces of said twophases to cause only superficial wetting of the total surface of theparticulate material and solubilization of soluble constituents of saidparticulate material wherein the amount of moisture to cause saidsuperficial wetting of the total surface of the particulate material iswithin the range of 0.7 - 4.0 percent of said particulate material,whereby a concentrated solution of said solid phase is formed, c.granulating said particulate materials in the presence of heat tocontrol the uniform growth of the granulated material into particleswherein at least 85 percent of the granulated particles are within therange of 6 to 20 mesh standard Tyler sieve size, and d. drying andcooling the granulated material.
 3. A process for the production ofgranulated materials which comprises: a. mixing at least one solidparticulate material selected from the group consisting of potassicsalts, nitrogeneous salts, phosphatic materials and mixtures thereofwith a liquid agent selected from the group consisting of water,nitrogeneous, phosphatic and potassic solutions, b. superficiallytreating the surface of said particulate material while continuouslymixing the same by applying thereto positive external forces of from20 - 80 POUNDS per square inch to cause only superficial wetting of thetotal surface of the particulate material and solubilization of solubleconstituents of said particulate material wherein the amount of moistureto cause said superficial wetting of the total surface of theparticulate material is within the range of 0.7 - 4.0 percent of saidparticulate material, and c. granulating said particulate material inthe presence of heat to control the uniform growth of the granulatedparticles.